Vibration-type actuators can be divided into standing-wave actuators and traveling-wave actuators in accordance with the type of vibration generated. FIG. 5 illustrates a control apparatus of a traveling-wave vibration-type actuator in the related art. A velocity signal obtained by a velocity detector 107 such as an encoder and a target velocity from a controller, which is not illustrated, are input to a velocity deviation detector 101, and a velocity deviation signal is output. The velocity deviation signal is input to a proportional-integral-derivative (PID) compensator 102 and output as a control signal.
The control signal output from the PID compensator 102 is input to a drive frequency pulse generator 103. A drive frequency pulse signal output from the drive frequency pulse generator 103 is input to a drive circuit 104, and a two-phase alternating voltage whose phases are different from each other by 90° is output. An alternating voltage is a two-phase alternating signal whose phases are different from each other by 90°. The alternating voltage output from the drive circuit 104 is input to an electromechanical energy conversion element of a vibration-type actuator 105, and a moving member of the vibration-type actuator 105 rotates at constant velocity. A driven member 106 (a gear, a scale, a shaft, and the like) connected to the moving member of the vibration-type actuator 105 is driven in such a way as to be rotated. The rotational speed of the driven member 106 is detected by a velocity detector 107 and feedback control is performed such that the rotational speed always becomes close to a target velocity.
As described above, when the rotational speed of a driven member (the same as the rotational speed of a moving member) is detected in the related art, it is necessary to use an optical encoder or the like and accordingly cost inevitably becomes high because of use of a scale and a photodetector. In addition, since a mounting space is needed, it is difficult to reduce the size. Therefore, a method for detecting the velocity without using an optical element such as an encoder is disclosed in PTL 1 and PTL 2.
In PTL 1, a method for detecting the amount of drive by utilizing a signal (hereinafter referred to as the “S-phase signal”) output from a vibration detection electrode included in a piezoelectric element is described, the method being realized by shaping a rotor, which is the moving member, in a certain way. Because the pressure at a portion of a vibrating member that is in contact with the rotor varies due to the eccentricity of the rotor, this method utilizes changes in the amplitude of the vibration detection electrode generated in accordance with the rotation of the rotor. Variations (one period per one rotation) in the pressure of the S-phase signal are subjected to signal processing using a low-pass filter, and then the number of pulses of a rectangular signal whose waveform has been shaped is counted in order to detect the amount of drive. As embodiments, a rotor whose circumferential surface is uneven, an eccentric rotor, a rotor provided with grooves, a rotor having a section whose friction coefficient is different, and the like are described.
In PTL 2, uneven portions are provided in a radial direction of a rotor. The amount of rotation of the rotor is detected by converting an envelope of height values of a drive current to a piezoelectric element emphasized by these uneven portions into a continuous or pulse signal. According to PTL 2, in order to generate a modulating component corresponding to the number of uneven portions of the rotor in the envelope of height values, it is necessary to combine the number of traveling waves and the number of protrusions of a vibrating member in the optimum condition.